Double-sided adhesive tape comprising a first outer, pressure-sensitive adhesive side, and a second outer side which can be thermally-activated

ABSTRACT

The invention relates to a double-sided adhesive tape having a first outer, pressure-sensitive adhesive side and a second outer, thermally-activatable side, and that comprises an at least dual-layered product construction consisting of layers A and B, layer A being a pressure-sensitive adhesive layer that is chemically cross-linked by thermal initiation, or being a pressure-sensitively adhesive carrier layer chemically cross-linked by thermal initiation, layer B being a thermoplastic synthetic material-based layer, layers A and B being in direct contact with one another, and the surface of layer A, which is in direct contact with layer B, having been corona or plasma pre-treated. The corona or plasma pre-treatment takes place in an atmosphere of nitrogen, carbon dioxide or a noble gas, or a mixture of at least two of these gases. The inventive adhesive tape is useful for adhesively bonding articles composed of thermoplastic polymer, of EPDM, or of another rubberlike material.

This application is a 371 of International Patent Application No.PCT/EP2012/058285, filed May 4, 2012, which claims foreign prioritybenefit under 35 U.S.C. §119 of the German Patent Application Nos. 102011 075 468.7, filed May 6, 2011, and 10 2011 075 470.9, filed May 6,2011, the disclosures of which are incorporated herein by reference.

The present invention relates to a double-sided adhesive tape having apressure-sensitive adhesive side and a heat-activatable side.

For industrial pressure-sensitive adhesive tape applications it is verycommon to use double-sided adhesive tapes in order to bond two materialsto one another. For the extremely wide variety of deployment slants therequirements are in some cases highly specific, and so exactingrequirements are imposed on the corresponding tapes. In the automobilesegment, for example, there is very often a requirement for hightemperature stability and also high resistance toward solvents andfuels. These properties are fulfilled in very good form by means ofcrosslinked pressure-sensitive acrylate adhesives (acrylate PSAs).

In the industrial segment likewise, moreover, the substrates that may bebonded vary very widely. Here it may in some cases be an advantage touse heat-activatable adhesives, which soften above a definedtemperature, flow very effectively onto the substrates, and then cool toproduce a firm assembly.

U.S. Pat. No. 6,124,032 B1, for example, describes a heat-activatableadhesive tape for sealing cartons. The requirements within this segment,however, are very forgiving, since the forces which act on the adhesivetape through the carton are relatively low. This is also reflected inthe carrier material, which consists of paper. The focus, therefore, isnot on bond strength but instead on a production method for aninexpensive pressure-sensitive adhesive tape.

U.S. Pat. No. 5,593,759 A describes a double-sided pressure-sensitiveadhesive tape which is composed of a carrier layer coated with two thinPSAs. The carrier layer consists of a structural adhesive. On thermalactivation, the PSA blends with the structural PSA, which likewise fullycures. By this route, very firm bonds between two adherends arepossible.

For many applications, nevertheless, this pressure-sensitive adhesivetape has an elementary disadvantage, since right from the start thedouble-sided pressure-sensitive adhesive tape is tacky on both sides.There are a host of applications for which it is an advantage if thepressure-sensitive adhesive tape at least on one side is nontacky andtherefore possesses optimum repositionability. In U.S. Pat. No.5,593,759 A this advantage is absent.

U.S. Pat. No. 4,248,748 A describes heat-activatable polyacrylate PSAswith additions of resin. The additions of resin raise the glasstransition temperature of the polyacrylate PSA and therefore the tack atroom temperature. The heat-activatable PSAs, however, are used only forsingle-sided pressure-sensitive adhesive tapes (film bonding, etc.).Hence no exacting requirements are imposed on the bonding of adherendsor on the anchorage of heat-activatable PSAs to the film.

U.S. Pat. No. 4,199,646 A describes heat-activatable pressure-sensitiveadhesive tapes, where the heat-activatable PSA has a modulus ofelasticity of 10 to 300 kg/cm². At the activation temperature,therefore, the modulus is situated at the level of PSAs at roomtemperature. In this patent as well—in analogy to U.S. Pat. No.4,248,748 A—the bond strength and the elasticity are controlled via thecomposition of the PSA. Moreover, only double-sided heat-activatablepressure-sensitive adhesive tapes are described, which can beheat-activated only on both sides.

EP 1 262 532 A1 describes a dual-function adhesive tape with aheat-activatable tackifier resin layer of polyolefin and with anacrylate PSA, the polyolefin layer being N₂ corona-treated to achievegood anchorage of the two layers to one another. The specificationdescribes only acrylate PSAs polymerized by irradiation with UV light. Adisadvantage of this is the limited coating rate, since polymerizationtakes place during the coating operation, and therefore monomerconversion and degree of polymerization are dependent on the coatingrate. The relatively high residual monomer contents may be a furtherproblem. It has emerged, moreover, that the N₂ corona treatment of thepolyolefin layer, in combination with PSAs other than the UV polymersdescribed, does not always lead to satisfactory results in terms of thebond strength between the PSA and the polyolefin.

In EP 0 384 598 A1 as well a dual-functional adhesive tape is described,with a heat-activatable tackifier resin layer of polyolefin and with anacrylate PSA polymerized by irradiation with UV light. In this case theanchorage to the polyolefin layer is achieved by means of agraft-polymerized monomer. A disadvantage here again is the limitedcoating rate, since here as well the UV light-initiated polymerizationoccurs during the coating operation, and hence monomer conversion anddegree of polymerization are not independent of the coating rate, andalso, furthermore, the grafting reaction takes place during the coatingoperation and is therefore likewise in correlation with the coatingrate.

EP 1 308 492 A1 describes a three-layer adhesive tape, the middle layerbeing a crosslinked polyurethane carrier material, and outer layer Abeing a heat-activatable adhesive. A disadvantage here is the anchoragebetween the heat-activatable outer layer A and the crosslinkedpolyurethane carrier material, especially after treatments under hot andhumid conditions, said anchorage not being of untrammeled quality forall areas of application.

Heat-activatable adhesive tapes can be used for producing compositearticles. EP 1 262 532 A1 describes one such composite article. Thedisadvantages arise from the above-depicted disadvantages of theadhesive tape described therein.

EP 0 679 123 B1 discloses a composite profile composed of an adhesivetape and a sealing profile. To form the composite assembly, a foamcarrier layer which is part of an adhesive tape is subjected there toincipient melting. A disadvantage is that as a result the foam loosesits foam structure, at least partially, and the adhesive tape thereforesuffers detractions from its characteristic adhesive qualities.

It is an object of the invention to satisfy the requirement for furtherheat-activatable adhesive tapes that do not exhibit the outlineddisadvantages of the prior art, or not to the same extent.

The adhesive tape is to have two different sides. One side is to bepressure-sensitively adhesive, the other side heat-activatable. Byheat-activatable is meant that the side is to soften or melt, or atleast partially melt, at higher temperatures, in order to be able toflow onto the substrate that is to be bonded, to melt onto thesubstrate, or to fuse with the substrate. The bond strength between thelayers of the adhesive tape is always to be of a quality such that onfailure of the adhesive tape there is never delamination between theindividual layers of the adhesive tape, but instead always a failurewithin a layer. This is to be the case even after treatment of theadhesive tape under hot and humid conditions. Very high layerthicknesses are to be obtainable, and are to be realizable in foamed orfoamlike form as well. Thick foamlike layers may greatly increase notonly the bond strength but also the shear strength of an adhesive tape.The adhesive tape is to hold reliably even at relatively hightemperatures, such as may typically occur in the interior of anautomobile. For economic reasons, the adhesive tape is to be produciblewith a high coating speed. The adhesive tape is to be suitable forproducing composite articles and for adhesively bonding EPDM profilesand other rubberlike profiles, more particularly sealing profiles in theautomobile segment.

These objects are achieved by means of an adhesive tape as set outaccording to the main claim. The dependent claims provide advantageousdevelopments of the adhesive tape, methods for producing same, andpossibilities for use.

The invention accordingly provides a double-sided adhesive tape having afirst outer pressure-sensitive adhesive side and a second outerheat-activatable side, comprising an at least two-layer product systemcomposed of layers A and B,

-   -   layer A being a layer of pressure-sensitive adhesive crosslinked        chemically by thermal initiation, or a pressure-sensitively        adhesive carrier layer crosslinked chemically by thermal        initiation,    -   layer B being a layer based on a thermoplastic polymer,    -   layer A and B being in direct contact with one another, and    -   the surface of layer A that is in direct contact with layer B        having been corona- or plasma-pretreated,    -   and the corona or plasma pretreatment has taken place in        atmosphere of nitrogen, carbon dioxide, or a noble gas, or a        mixture of at least two of these gases.

Surprisingly it has been found that double-sided adhesive tapes of thiskind, with a pressure-sensitively adhesive side and a heat-activatableside, meet the requirements to outstanding effect.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe drawings, wherein:

FIG. 1 is a schematic of one embodiment of the adhesive tape accordingto the present invention, this one comprising an at least two-layerproduct construction composed of the layers A and B;

FIG. 2 is a schematic of another embodiment of the adhesive tapeaccording to the present invention, this one comprising a layer C inaddition to layers A and B; and

FIG. 3 is a schematic of another embodiment of the adhesive tapeaccording to the present invention, this one comprising multilayer layerD, including layer E, in addition to layers A and B.

Layer A is a layer of pressure-sensitive adhesive that is crosslinkedchemically by thermal initiation, or is a pressure-sensitively adhesivecarrier layer crosslinked chemically by thermal initiation. A layer ofpressure-sensitive adhesive or a pressure-sensitively adhesive layermeans, in this specification as in general linguistic usage, a layerwhich—especially at room temperature—is durably tacky and also adhesive.This layer may be an outer, tangible layer of an adhesive tape, and mayalso be a middle layer which is therefore visible and perceptible onlyat the outside edges. Characteristic of such a layer is that it can beapplied to a substrate by means of pressure, and remains adhering there,with the pressure to be employed and the duration of that pressure notbeing defined in more detail. In certain cases, depending on the precisenature of the PSA, on the temperature and the atmospheric humidity, andon the substrate, a minimal pressure acting for a short time, which doesnot go beyond a gentle contact for a brief moment, is sufficient toobtain the adhesion effect; in other cases, a longer-term duration ofexposure to a high pressure may also be necessary.

PSA layers or pressure-sensitively adhesive layers have particular,characteristic viscoelastic properties, which result in the durable tackand adhesiveness.

These layers, characteristically, when mechanically deformed, give riseboth to viscous flow processes and also to the development of elasticresilience forces. In terms of their respective fraction, the twoprocesses are in a particular relationship with one another, dependentnot only on the precise composition, structure, and degree ofcrosslinking of the PSA layer in question, but also on the rate andduration of the deformation, and on the temperature.

The proportional viscous flow is necessary for the achievement ofadhesion. Only the viscous components, produced by macromolecules withrelatively high mobility, allow effective wetting and effective flowonto the substrate to be bonded. A high viscous flow component resultsin high pressure-sensitive adhesiveness (also referred to as tack orsurface tackiness) and hence often also in a high bond strength. Owingto a lack of flowable components, highly crosslinked systems, orpolymers which are crystalline or have undergone glasslikesolidification, generally have at least little tack, or none at all.

The proportional elastic resilience forces are necessary for theachievement of cohesion. They are brought about, for example, by verylong-chain, highly entangled macromolecules and also by physically orchemically crosslinked macromolecules, and permit transmission of theforces engaging on an adhesive bond. Their result is that an adhesivebond is able to withstand sufficiently over a prolonged time period along-term load acting on it, in the form for example of a sustainedshearing load.

For a more precise description and quantification of the extent ofelastic and viscous components, and also of the ratio of the componentsto one another, it is possible to employ the variables of storagemodulus (G′) and loss modulus (G″), which can be determined by means ofDynamic Mechanical Analysis (DMA). G′ is a measure of the elasticcomponent, G″ a measure of the viscous component, of a substance and ofthe layer produced from it. Both variables are dependent on thedeformation frequency and the temperature.

The variables can be determined by means of a rheometer. In this case,the material in layer form for analysis is exposed to a sinusoidallyoscillating shearing stress in—for example—a plate/plate arrangement. Inthe case of instruments operating with shear stress control, thedeformation is measured as a function of time, and the time offset ofthis deformation relative to the introduction of the shearing stress ismeasured. This time offset is identified as phase angle δ.

The storage modulus G′ is defined as follows: G′=(τ/γ)*cos(δ) (τ=shearstress, γ=deformation, δ=phase angle=phase shift between shear stressvector and deformation vector). The definition of the loss modulus G″ isas follows: G″=(τ/γ)*sin(δ) (τ=shear stress, γ=deformation, δ=phaseangle=phase shift between shear stress vector and deformation vector).

A substance and the layer produced from it are generally considered tobe pressure-sensitively adhesive, and are defined for the purposes ofthis specification as being pressure-sensitively adhesive, if at roomtemperature, here by definition at 23° C., in the deformation frequencyrange from 10⁰ to 10¹ rad/sec, G′ is at least partly in the range from10³ to 10⁷ Pa and if G″ is likewise at least partly within that range.Substances of this kind are occasionally referred to as viscoelasticsubstances, and the layers produced from them as viscoelastic layers. Inthis specification, the terms “pressure-sensitively adhesive” and“viscoelastic” are considered to be synonymous. Reference to apressure-sensitively adhesive carrier layer, accordingly, in thisspecification means a viscoelastic carrier layer within the statedlimits for G′ and G″.

A layer of pressure-sensitive adhesive or a pressure-sensitivelyadhesive carrier layer is chemically crosslinked if the PSA layer orpressure-sensitively adhesive carrier layer has attained, throughchemical reaction with a crosslinker, a state which renders it no longermeltable and no longer soluble in organic solvents. Liquefaction is thenpossible only through decomposition which is irreversible. Crosslinkerscontemplated include all at least difunctional substances which are ableto enter into chemical crosslinking reactions with the functional groupsof the PSA. Their selection is guided by the functional groups of thePSA. PSAs which carry carboxyl groups are typically crosslinked withdiepoxides or polyepoxides, possibly with additional catalysis, by, forexample, tertiary amines, or with metal acetylacetonates, metalalkoxides, and alkoxy-metal acetylacetonates. For the crosslinking ofPSAs which carry hydroxyl groups, diisocyanates or polyisocyanates areappropriate examples.

The term “thermal initiation” indicates that the crosslinker or thecrosslinker system, consisting of crosslinker, accelerator and/orinitiator, enters into, or initiates, the chemical crosslinking reactionby temperature exposure, and not by radiation exposure. Thisspecification reckons the thermally initiated crosslinking forms toinclude the systems where the activating energy can be overcome even atroom temperature or below room temperature without additionalapplication of radiation—in other words, crosslinking forms whichproceed even at room temperature or below.

The crosslinking reactions in this invention, then, are initiated not byactinic radiation or by ionizing radiation such as, for instance, UVrays, X-rays, or electron beams. In one preferred embodiment of thisinvention, additional crosslinking forms, initiated by actinic or byionizing radiation, are excluded, since surprisingly it has been foundthat the bond strength between the layers A and B of the adhesive tapemay be impaired in certain cases by additional exposure to actinic orionizing radiation.

In one preferred method, layer A is produced in a hotmelt process, moreparticularly an extrusion process. For this purpose, thepressure-sensitively adhesive material from which the PSA layercrosslinked chemically by thermal initiation, or thepressure-sensitively adhesive carrier layer A crosslinked chemically bythermal initiation, is to be produced, is introduced in the melted stateinto a continuously operating mixing assembly, preferably an extruder.Also introduced into the continuously operating mixing assembly is thecrosslinker system, and the so the crosslinking reaction is commenced.This is followed by the melt, which at this point in time is still notcrosslinked, being discharged from the mixing assembly and beingimmediately coated and shaped to form the layer A. The crosslinkingreaction that has been commenced progresses in the meantime, and so ashort time later, layer A has attained its crosslinked state. Theprincipal advantages of this method are that high coating speeds can berealized and that the layers that can be produced are thicker than witha solvent-based method. Surprisingly, layers (A) produced by a method ofthis kind can be attached in accordance with the invention with highbond strength to thermoplastic layers (B).

In an advantageous development of the invention, layer A is foamed orhas a foamlike consistency. The foam or the foamlike consistency mayhave been produced by the introduction or chemical generation of one ormore gases into the polymer matrix, or through the use of solid glassmicrospheres, hollow glass microspheres and/or plastic microspheres ofany kind. Mixtures of the substances stated may also be used. Theplastic microspheres may be used in preexpanded form or in an expandableform. The plastic microspheres, also called microballoons, are hollowelastic spheres which have a thermoplastic polymer shell; consequentlythey are also referred to as expandable polymeric microspheres. Thesespheres are filled with low-boiling liquids or liquefied gas. Shellmaterial used includes, in particular, polyacrylonitrile, polyvinyldichloride (PVDC), polyvinyl chloride (PVC), polyamides, orpolyacrylates. Suitable low-boiling liquids are, in particular,hydrocarbons of the lower alkanes, as for example isobutane orisopentane, which are enclosed under pressure as liquefied gas in thepolymer shell. By action on the microballoons, more particularly by theaction of heat—especially through supply of heat or generation of heat,as for example by means of ultrasound or microwave radiation—there issoftening of the outer polymer shell. At the same time, the liquidpropellant gas contained within the shell changes into its gaseousstate. For a particular pairing of pressure and temperature—termed“critical pairing” for the purposes of this specification—themicroballoons undergo irreversible, three-dimensional expansion.Expansion is at an end when the internal pressure equals the externalpressure. Since the polymeric shell is retained, a closed-cell foam isobtained in this way.

A host of types of microballoon are available commercially, such as, forexample, from Akzo Nobel, the Expancel DU (dry unexpanded) products,which differ essentially in their size (6 to 45 μm diameter in theunexpanded state) and their required expansion onset temperature (75° C.to 220° C.).

Furthermore, unexpanded microballoon products are also available inaqueous dispersion form with a solids fraction or microballoon fractionof about 40 to 45 weight %, and also in the form of polymer-boundmicroballoons (masterbatches), in ethyl-vinyl acetate, for example, witha microballoon concentration of about 65 weight %. Obtainable,furthermore, are microballoon slurry systems, in which the microballoonsare present with a solids fraction of 60 to 80 weight % in the form ofan aqueous dispersion. The microballoon dispersions, the microballoonslurries, and the masterbatches, like the DU products, are suitable forfoaming in line with the advantageous development of the invention.

As a result of their flexible, thermoplastic polymer shell, the foamsproduced using microballoons posses a higher crack-bridging capacitythan those filled with unexpandable, nonpolymeric hollow microspheres(such as hollow glass or ceramic spheres). They are therefore moresuitable for compensating manufacturing tolerances of the kind thatoccur in the case of injection moldings, for example. Furthermore, afoam of this kind is able better to compensate thermal stresses.

Accordingly, through the selection of the thermoplastic resin of thepolymer shell, for example, further influence may be exerted over themechanical properties of the foam. Hence it is possible, for example, toproduce foams with a higher cohesive strength than with the polymermatrix alone, despite the foam having a lower density than the matrix.Moreover, typical foam properties, such as the capacity to conform torough substrates, can be combined with a high cohesive strength for PSAfoams.

Preferably up to 30 weight % of microballoons, more particularly between0.5 weight % and 10 weight %, based on the overall formula of thepolymer composition without microballoons, are added for foaming to thepolymer composition that is to be foamed.

In one preferred embodiment, layer A is a layer based on a knownpolyacrylate PSA crosslinked chemically by thermal initiation. Suitablecrosslinkers for polyacrylate PSAs are diisocyanates or polyisocyanates,more particularly dimerized or trimerized isocyanates, diepoxide orpolyepoxide compounds, epoxide-amine crosslinker systems, and, forcoordinative crosslinking, metal acetylacetonates, metal alkoxides, andalkoxy-metal acetylacetonates, in each case in the presence offunctional groups in the polymer macromolecules that are able to reactwith isocyanate groups and/or epoxide groups and also to enter intocoordinative bonds with the metal compounds.

Advantageous crosslinker systems and suitable methods to allowprocessing of the polymer composition in the melt with such crosslinkersare described in, for example, the specifications EP 0 752 435 A, EP 1802 722 A, EP 1 791 921 A, EP 1 791 922 A, EP 1 978 069 A, and DE 102008 059 050 A. The disclosure content to this effect is thereforeincorporated explicitly into the disclosure content of the presentspecification. The crosslinker or, in the case of crosslinker systems,at least one constituent of the crosslinker system (for example, eitherthe crosslinker or the accelerator) is added to the melt only at a latestage and is immediately mixed in very homogeneously (by means ofefficient mixing, in the extruder, for example), in order to make theresidence time of the reactive system in the polymer melt very short andtherefore the processing life (“pot life”) as long as possible. The keypart of the crosslinking reaction takes place only after the polymer hasbeen shaped, more particularly after it has been shaped to form thelayer, and preferably at room temperature. As a result of thisprocedure, two methodological aspects can be optimized with respect toone another, namely, on the one hand, a minimal crosslinking reactionprior to shaping, in order largely to avoid unwanted and uncontrolledpreliminary crosslinking and the corresponding gelling (formation ofmore highly crosslinked regions—for example, gel specks—within thepolymer melt), but on the other hand an extremely high mixing efficiencyon the part of the crosslinker or crosslinking system components in therelatively short residence time in the polymer melt prior to coating, inorder in fact to guarantee a very homogeneously crosslinked end product.

Having emerged as being particularly preferred, especially for thecrosslinking of polyacrylate PSAs with functional groups suitable forentering into linking reactions with epoxide groups, is acrosslinker-accelerator system comprising at least oneepoxide-group-containing substance as crosslinker and as accelerator atleast one substance which has an accelerating effect on the linkingreaction at a temperature below the melting temperature of thepolyacrylate. Examples of suitable epoxide-group-containing substancesinclude polyfunctional epoxides, especially difunctional ortrifunctional epoxides (i.e., those having two or three epoxide groups,respectively), but also epoxides of higher functionality, or mixtures ofepoxides with different functionalities. Accelerators which can be usedwith preference are amines (to be interpreted formally as substitutionproducts of ammonia), examples being primary and/or secondary amines;more particularly, tertiary and/or polyfunctional amines are used. It isalso possible to employ amines which have a plurality of amine groups,it being possible for these amine groups to be primary and/or secondaryand/or tertiary amine groups, and more particularly diamines, triaminesand/or tetramines. Selected more particularly are amines which do notenter into any reactions, or only into slight reactions, with thepolymer building blocks. Further examples of accelerators which can beused are those with a phosphate basis, such as phosphines and/orphosphonium compounds.

By means of this method it is possible for polymers in particular basedon acrylic esters and/or methacrylic esters to be both foamed andcrosslinked, with advantageously at least some of the acrylic esterscontaining the functional groups, and/or comonomers being present whichcontain the functional groups. Suitable functional groups of the polymerto be crosslinked, especially (meth)acrylate-based, are, in particular,acid groups (carboxylic acid, sulfonic acid and/or phosphonic acidgroups) and/or hydroxyl groups and/or acid anhydride groups and/orepoxide groups and/or amine groups, these groups being selected and moreparticularly attuned to the particular crosslinker. It is especiallyadvantageous if the polymer contains copolymerized acrylic acid and/ormethacrylic acid.

In another preferred embodiment, layer A is a layer based on a knownpolyurethane PSA crosslinked chemically by thermal initiation.Polyurethane PSAs crosslinked accordingly are described in, for example,EP 1 469 024 A1, EP 1 469 055 B1, EP 1849811 B1, or in EP 2 046 855 A1.Pressure-sensitively adhesive polyurethane hotmelt prepolymers which canbe processed and crosslinked in an extrusion process are described in EP2 276 784 A1. Particularly suitable crosslinkers for polyurethane PSAsare diisocyanates or polyisocyanates, more particularly dimerized ortrimerized isocyanates.

One particular crosslinking system is described in EP 2 325 220 A1. Aprocess for producing a chemically crosslinked polyurethane film isdescribed in EP 2 119 735 A1. The disclosure content of thesespecifications is explicitly incorporated into the disclosure content ofthe present invention.

Not only the advantageous polyacrylate PSAs but also the advantageouspolyurethane PSAs may include further formulating ingredients such as,for example, fillers, resins, especially tackifying resins,plasticizers, flame retardants, aging inhibitors (antioxidants), lightstabilizers, UV absorbers, rheological additives, and also otherauxiliaries and adjuvants.

The outer surface of the layer B, which is identical to the second outerside of the adhesive tape, is heat-activatable. By heat-activatable ismeant that this outer surface, at relatively high temperatures,undergoes softening or melting or at least partial softening or melting,in order to be able to flow onto the substrate that is to be bonded, tomelt onto the substrate, or to fuse with the substrate.

Layer B is a layer based on a thermoplastic polymer and is therefore athermally deformable, meltable, and weldable layer, the operations ofdeforming, melting, and welding being reversible and repeatable.

Preferred thermoplastic polymers are polyamide, polyesters,thermoplastic polyurethane, and polyethylene-vinyl acetate. Particularlypreferred, especially for the bonding of EPDM profiles and other rubberprofiles, are polyolefins or polyolefin copolymers or mixtures of thestated substances, more particularly polypropylene copolymers.Particularly preferred are ethylene-propylene copolymers or mixtures ofethylene-propylene copolymers and other polyolefins.

An ethylene-propylene copolymer particularly preferred for producing anassembly composed of the adhesive tape of the invention and a profilemade EPDM or of another rubberlike material, by hot sealing of theheat-activatable side of the adhesive tape onto the profile, has amelting temperature as determined by DSC of between 140° C. inclusiveand 180° C. inclusive, preferably between 150° C. inclusive and 170° C.inclusive. The abbreviation DSC stands for the known thermoanalyticalmethod of “differential scanning calorimetry”, DIN 53765.

The surface of the layer A, in other words the PSA layer crosslinkedchemically by thermal initiation or the pressure-sensitively adhesivecarrier layer crosslinked chemically by thermal initiation, and indirect contact with layer B, has been corona- or plasma-pretreated priorto the establishment of said contact, the corona pretreatment or plasmapretreatment having taken place in an atmosphere of nitrogen, carbondioxide, or a noble gas, or in a mixture of at least two of these gases.

Corona pretreatment refers to surface treatment with filamentarydischarges that is generated by high alternating voltage between twoelectrodes, with the discrete discharge channels impinging on thesubstrate surface to be treated. More particularly, the term “corona”usually refers to “dielectric barrier discharge” (DBD). In this case atleast one of the electrodes consists of a dielectric, in other words aninsulator, or is covered or coated with such a material.

Corona pretreatment, as method for surface pretreatment, is known priorart (in this regard, see also Wagner et al., Vacuum, 71 (2003), 417-436)and is much in use industrially. Without further qualification, theassumed process gas is ambient air, but that is not the case in thisinvention. The use of process gases other than air, such as nitrogen,carbon dioxide, or noble gases, for example, is likewise known in theform of prior art.

The substrate is placed in or guided through the discharge space betweenan electrode and a counterelectrode, this being defined as directphysical treatment. Substrates in web form are typically conveyedbetween an electrode and a grounded roll.

By means of a suitably high web tension, the substrate is pressed ontothe counterelectrode, in the latter's roll configuration, in order toprevent air inclusions. The treatment distance is typically about 1 to 2mm. A fundamental disadvantage of a two-electrode geometry of this kind,with treatment in the space between electrode and counterelectrode, isthe possible reverse-face treatment. In the case of very smallinclusions of air or gas on the reverse face, as for example if the webtension is too low in the case of a roll-to-roll treatment, there isusually unwanted corona treatment of the reverse face.

Although in the wider sense a corona treatment in air is a technology inwhich plasma plays a part, a narrower definition is usually understoodfor plasma treatment at atmospheric pressure.

If a corona treatment takes place in a gas mixture other than air, asfor example a nitrogen-based gas mixture, the term “plasma” is indeed inpart appropriate. A plasma treatment at atmospheric pressure in thenarrower sense, however, is a homogenous and discharge-free treatment.By use of noble gases, in some cases with admixtures, a plasma of suchhomogeneity can be produced, for example. In this case the treatmenttakes place in a flat, homogeneously plasma-filled reaction space.

The reactive plasma contains radicals and free electrons which are ableto react rapidly with many chemical groups in the substrate surface.This leads to the formation of gaseous reaction products and to highlyreactive free radicals in the surface. Through secondary reactions withother gases, these free radicals are able rapidly to undergo furtherreaction, and they form different chemical functional groups on thesubstrate surface. As with all plasma technologies, the generation offunctional groups competes with the breakdown of the material.

The substrate to be treated, instead of being exposed to the reactionspace of a two-electrode geometry, may also be exposed only to thedischarge-free plasma (“indirect” plasma). To a good approximation, inthat case, the plasma is usually also free of potential. In this casethe plasma is usually expelled from the discharge zone by a flow of gas,and, after a short distance, guided onto the substrate. The lifetime(and hence also the useful distance) of the reactive plasma, oftencalled “afterglow”, is determined by the precise details of therecombination reactions and of the plasma chemistry. The reactivity isusually observed to decline exponentially with the distance from thedischarge source.

Modern indirect plasma technologies are often based on a nozzleprinciple. The nozzle here may be of round or linear configuration; insome cases, rotary nozzles are operated—there is no desire here toimpose any restriction. A nozzle principle of this kind is advantageouson account of its flexibility and its inherently single-sided treatment.Such nozzles, from the company Plasmatreat GmbH (Germany), for example,are widespread in industry for the pretreatment of substrates prior toadhesive bonding. Disadvantages are the indirect treatment, which, beingdischarge-free, is less efficient, and hence the reduced web speeds. Thecustomary constructional form of a round nozzle, however, is especiallysuitable for treating narrow webs of product, such as an adhesive tapewith a breadth of a few cm, for example.

There are a variety of plasma generators on the market, differing in theplasma generation technology, the nozzle geometry, and the gasatmosphere. Although the treatments differ in factors including theefficiency, the fundamental effects are usually similar and aredetermined above all by the gas atmosphere employed. Plasma treatmentmay take place in different atmospheres, with this invention havingfound nitrogen, carbon dioxide, or a noble gas, or a mixture of at leasttwo of these gases, to constitute a suitable atmosphere.

In principle it is also possible to admix the atmosphere with coating orpolymerizing constituents, in the form of gas (ethylene, for example) orliquids (in atomized form as aerosol). There is virtually no restrictionon the aerosols that are suitable. The indirectly operating plasmatechnologies in particular are suitable for the use of aerosols, sincethere is no risk of fouling of the electrodes.

Since the effects of a plasma treatment are of chemical nature and thefocus is on changing the surface chemistry, the methods described abovemay also be described as chemical-physical treatment methods. Althoughthere may be differences in the detail, no particular technique is to beemphasized for the purposes of this invention, in terms neither of thenature of the plasma generation nor of the mode of construction.

Plasma pretreatment in this specification means an atmospheric-pressureplasma pretreatment. Defined as atmospheric-pressure plasma in thisspecification is an electrically activated, homogeneous, reactive gaswhich is not in thermal equilibrium, with a pressure close to theambient pressure. As a result of the electrical discharges and ofionization processes in the electrical field, the gas is activated, andhighly excited states are generated in the gas constituents. The gasused or the gas mixture is referred to as process gas. In principle theplasma atmosphere may also be admixed with coating or polymerizingconstituents, in the form of gas or aerosol.

The term “homogeneous” points to the fact that no discrete,inhomogeneous discharge channels impinge on the surface of the substrateto be treated (although they may be present in the generation space).

The restriction “not in thermal equilibrium” means that the temperatureof the ions may differ from the temperature of the electrons. In thecase of thermally generated plasma, these would be at equilibrium (inthis regard, see also, for example, Akishev et al., Plasmas andPolymers, vol. 7, No. 3, September 2002).

With regard to the inventive atmosphere of nitrogen, carbon dioxide, ora noble gas, or of a mixture of at least two of these gases, it shouldbe ensured that there are no—or at any rate only very small—fractions ofresidual oxygen present in this atmosphere. Target oxygen fractions arenot more than 1000 ppm, preferably not more than 100 ppm, morepreferably not more than 10 ppm.

The intensity of a corona treatment is reported as the “dose” in[Wmin/m²], where the dose D=p/b*v, where P=electrical power [W],b=electrode breadth [m], and v=web speed [m/min].

The corona pretreatment takes place preferably with a dose of 1 to 150W*min/m². Particularly preferred is a dose from 10 to 100 W*min/m², moreparticularly a dose from 20 to 80 W*min/m².

The corona or plasma pretreatment of the surface of the layer A that isin contact with layer B takes place preferably in the already chemicallycrosslinked state of the layer A, in other words at a point in time whenthe crosslinking reaction proceeding by means of thermal initiation hasalready advanced to such an extent that layer A is no longer meltable.At this point in time, however, the crosslinking must not have beenfully concluded, although it may be so. It has emerged, surprisingly,that the anchorage between the layers A and B is especially good and isable to bear diverse loads when the corona or plasma pretreatment hastaken place following attainment of the crosslinked state.

In accordance with the invention, layer A and layer B are in directcontact with one another. This means that between the corona- orplasma-pretreated surface of the layer A that is in direct contact withlayer B, no additional, further substances or layers are attached or arelocated there. Direct contact, accordingly, entails no additionaladhesive, PSA, adhesion-promoting substance, or other substance beinglocated or introduced between layer A and layer B. The direct contactbetween layer A and layer B is produced by a conventional backing orlaminating procedure, preferably at room temperature. The backing orlaminating procedure takes place preferably directly after the corona orplasma pretreatment at the surface of the layer A, without layer Ahaving been lined with a release liner beforehand, and without layer A,if it is in web form, having been enclosed in a release liner and woundup. Ideally only a few seconds elapse between the corona or plasmapretreatment of the surface of the layer A, and the backing orlaminating procedure.

The surface of the layer B, i.e., the layer based on a thermoplasticpolymer that is in direct contact with layer A, may be aircorona-pretreated before this contact is produced.

In order to obtain optimized adhesion to difficult-to-bond surfaces,such as, for example, to low-energy surfaces such as polyethylene orpolypropylene, for instance, or to certain coated surfaces such as, forinstance, certain types of clearcoat, the surface of the layer A that isnot in direct contact with layer B may be in direct contact with afurther layer (layer C, FIG. 2) or with a further layer sequence (layersequence D, FIG. 3), the outer layer of the layer sequence being a PSAlayer (layer E, FIG. 3), which in that case is designed for the specificuse. A layer sequence (D) may be necessary in order, for example, toobtain optimum anchorage between the outer, pressure-sensitivelyadhesive layer (E) and the layer A of the invention, in order to preventmigration phenomena, or to produce an extremely flatpressure-sensitively adhesive surface. Individual layers in the layersequence, accordingly, may be adhesion-promoting layers, barrier layers,or smoothing layers, for example. The outer, pressure-sensitivelyadhesive surface of the adhesive tape may likewise be corona- orplasma-treated for the purpose of achieving optimized adhesion todifficult-to-bond substrates.

The double-sided adhesive tape of the invention, having a first outerpressure-sensitively adhesive side and a second outer heat-activatableside, comprising an at least two-layer product construction composed ofthe layers A and B, as shown in FIG. 1, with layer A being a PSA layercrosslinked chemically by thermal initiation or being apressure-sensitively adhesive carrier layer crosslinked chemically bythermal initiation, and layer B being a layer based on a thermoplasticpolymer, with layer A and layer B being in direct contact with oneanother, and with the surface of the layer A that is in direct contactwith layer B having been corona- or plasma-pretreated, characterized inthat the corona or plasma pretreatment has taken place in an atmosphereof nitrogen, carbon dioxide, or a noble gas, or of a mixture of at leasttwo of these gases, exhibits a combination of outstanding productproperties such as could not have been foreseen even by the skilledperson. Thus the adhesive tape has a high internal bond strength, inother words a high bond strength between the layers A and B. The heightof the bond strength is such that destructive loads on the adhesivetape, as in the course of peel tests or shear tests, for example, doesnot generally result in splitting between the layers A and B. Instead,generally speaking, there is a rupture of material within the layer Aor—depending on the substrate used and on the PSA used—there is adhesivefailure between the adhesive tape and the bonded substrate. This is alsothe case when the adhesive tape, as intended, has been laminated hotonto a substrate, at temperatures of 150° C. to 200° C., for example.This has no adverse effect on the bond strength between the layers A andB. After treatments under hot and humid conditions as well, as forexample after two-week storage under conditions of 85° C. and 85%relative humidity, the high bond strength is retained, as it is aftertwo-week storage under alternating conditions, with cycles of 4 hours−40° C., 4 hours heating/cooling, 4 hours 80° C./80% relative humidity.Furthermore, the bond strength is also retained when the destructivetests are performed at elevated temperatures, as for example at 70° C. Aproviso is that the testing temperature does not exceed the meltingtemperature of the layer B.

The double-sided adhesive tape of the invention can be produced in amanner such that the polymerization of the PSA or of thepressure-sensitively adhesive carrier layer, and their crosslinking,take place in a process decoupled from that of coating. In this way,very economic production operations with high coating speeds can bepresented.

Moreover, the double-sided adhesive tape of the invention can beproduced advantageously in very thick layers and also with a foamedlayer. The adhesive tape, accordingly, is able to perform, for example,gap-bridging sealing functions or contributions to noise suppression.

With the double-sided adhesive tape of the invention, very high bondstrengths can be realized, of 50 or more N/cm. It is also possible toobtain very high shear strengths. Contributions to this may come veryadvantageously from the foaming, and also from the high thicknesses thatare realizable.

With the double-sided adhesive tape of the invention, composite articlescan be produced that are composed of this adhesive tape and an articlemade of a thermoplastic polymer, of EPDM, or of another rubberlikematerial.

The double-sided adhesive tape of the invention is suitable foradhesively bonding profiles of EPDM or of another rubberlike material.

The examples below are intended to describe the invention in moredetail, without any intention for the invention to be restrictedthereby.

The test methods below were used to provide brief characterization ofthe specimens produced in accordance with the invention:

Peel Strength

The peel strength was determined in accordance with PSTC-101. Thedetermination took place under test conditions of 23° C.+/−1° C.temperature and 50%+/−5% relative humidity. An assembly was producedfrom the adhesive tape of the invention and a test substrate selected inline with the thermoplastic polymer used for the layer B. The testsubstrates were always selected from the same type of polymercorresponding to the particular thermoplastic polymer used for the layerB. Where, for example, the thermoplastic polymer of layer B was apolyurethane, therefore, a thermoplastic polyurethane test substrate wasselected as well. In the case of the polypropylene products,additionally, commercial EPDM profiles of different Shore A hardnesses,from Meteor Gummiwerke, were used as test substrates.

The assembly was produced by hot lamination of the adhesive tape of theinvention, by its layer B, onto the test substrate. The requiredtemperature was produced using a hot-air blower and was dependent on thethermoplastic polymer used for the layer B.

A strip of aluminum was mounted on layer A. The adhesive tape of theinvention was incised with a scalpel close to the substrate and thenclamped, together with the aluminum strip, into the jaws of a tensiletesting machine. Tearing apart or peeling took place using rubberlikesubstrates, in a geometry which, when viewed from the side, resembles arecumbent “T”. Where solid, stiff substrates were used, peeling tookplace at an angle of 90°. The peel rate was 300 nm/min.

The objective was to ascertain whether there is a weakness in assemblybetween layers A and B or whether the failure occurs within a layer, andthe extent of the failure force.

Shear Test

The shear test was carried out in accordance with test specificationPSTC-107. The test specimens were prepared by welding two adhesive tapestrips of the invention to one another via their layers D, by hotlamination using a hot-air blower, to produce a double-sidedlypressure-sensitively adhesive tape specimen. This double-sidedlypressure-sensitively adhesive tape specimen was bonded between two steelplates (stainless steel 302 to ASTM A 666; 50 mm×125 mm×1.1 mm, brightannealed surface; surface roughness 50±25 mm mean arithmetic deviationfrom the baseline), pressed on four times with a 2 kg weight, and thenexposed to a sustained, constant shearing load selected such that theadhesive tape specimen fails after a relatively long time.Determinations were made of whether there is a weakness in assemblybetween the layers A and B, or whether the failure occurs within alayer, and the length, in minutes, of the holding power.

The bond area was 13×20 mm² in each case. The shearing load on this bondarea was 2 kg. Measurement took place at room temperature (23° C.) andin some cases at 70° C. as well.

Aging Characteristics

The assemblies of the adhesive tape of the invention and a substrate, aswere produced for the measurement of the peel strength, were subjectedto storage under selected conditions, in order to ascertain the agingcharacteristics.

Storage a): Two-week storage under conditions of 85° C. and 85% relativehumidity

Storage b): Two-week storage under cyclical conditions, with thefollowing cycles: 4 hours −40° C., 4 hours heating/cooling, 4 hours 80°C./80% relative humidity.

When the storage time was up, the samples were subjected to the peelstrength test.

Static Glass Transition Temperature

The static glass transition temperature is determined by dynamicscanning calorimetry in accordance with DIN 53765. The figures for aglass transition temperature T_(g) are based on the glass transformationtemperature value T_(g) according to DIN 53765: 1994-03, unlessindicated otherwise in any specific case.

Molecular Weights

The average molecular weight M_(w) and the average molecular weightM_(n), and the polydispersity D, were determined by means of gelpermeation chromatography (GPC). The eluent used was THF with 0.1 vol %trifluoroacetic acid. Measurement took place at 25° C. The preliminarycolumn used was a PSS-SDV, 5 μm, 10³ Å (10⁻⁷ m), ID 8.0 mm×50 mm.Separation took place using the columns PSS-SDV, 5 μm, 10³ Å (10⁻⁷ m),10⁵ Å (10⁻⁵ m), and 10⁶ Å (10⁻⁴ m), each with ID 8.0 mm×300 mm. Thesample concentration was 4 g/l, the flow rate 1.0 ml per minute.Measurement took place against PMMA standards.

The raw materials used for preparing polyacrylate PSAs were as follows:

Chemical compound Trade name Manufacturer CAS No.Bis(4-tert-butylcyclohexyl) Perkadox 16 Akzo Nobel 15520-11-3peroxydicarbonate 2,2′-Azobis(2-methylpropionitrile), Vazo 64 DuPont78-67-1 AIBN 2,2′-Azobis(2-methylbutyronitrile) Vazo 67 DuPont13472-08-7 Pentaerythritol tetraglycidyl ether Polypox R16= UPPC AG3126-63-4 3,4-Epoxycyclohexylmethyl 3,4- Uvacure 1500 Cytec 2386-87-0epoxycyclohexanecarboxylate Industries Inc. Triethylenetetramine Epikure925 Hexion 112-24-3 Specialty Chemicals Microballoons (MB) Expancel 051Expancel (dry unexpanded microspheres, DU 40 Nobel diameter 9 to 15 μm,expansion Industries onset temperature 106 to 111° C., TMA density ≦ 25kg/m³) Terpene-phenolic resin (softening Dertophene T110 DRT resins25359-84-6 point 110° C.; M_(w) = 500 to 800 g/mol; D = 1.50) Acrylicacid n-butyl ester n-Butyl acrylate Rohm & Haas 141-32-2 Acrylic acidAcrylic acid, pure BASF 79-10-7 2-Ethylhexyl acrylate Brenntag 103-11-7Methyl acrylate BASF 96-33-3

The expansion capacity of the microballoons can be described through thedetermination of the TMA density [kg/m³] (Stare Thermal Analysis Systemfrom Mettler Toledo; heating rate 20° C./min). This TMA density is theminimum achievable density at a defined temperature T_(max) underatmospheric pressure before the microballoons collapse.

An example polvacrvlate PSA 1 (abbreviated designation in the examples:AC1) was prepared as follows: a reactor conventional for radicalpolymerizations was charged with 54.4 kg of 2-ethylhexyl acrylate, 20.0kg of methyl acrylate, 5.6 kg of acrylic acid, and 53.3 kg ofacetone/isopropanol (94:6). After nitrogen gas had been passed throughthe reactor for 45 minutes, with stirring, the reactor was heated to 58°C. and 40 g of Vazo 67, in solution in 400 g of acetone, were added.Thereafter the external heating bath was heated to 75° C. and thereaction was carried out constantly at this external temperature. After1 hour a further 40 g of Vazo 67, in solution in 400 g of acetone, wereadded, and after 4 hours the batch was diluted with 10 kg ofacetone/isopropanol mixture (94:6). After 5 hours and again after 7hours, initiation was repeated with 120 g portions ofbis(4-tert-butylcyclohexyl)peroxydicarbonate, in each case in solutionin 400 g of acetone. After a reaction time of 22 hours, thepolymerization was discontinued and the batch was cooled to roomtemperature. The product had a solids content of 55.9% and was freedfrom the solvent under reduced pressure in a concentrating extruder(residual solvent content ≦0.3 weight %). The resulting polyacrylate hada K value of 58.8, an average molecular weight of M_(w)=746 000 g/mol, apolydispersity of D (M_(w)/M_(g))=8.9, and a static glass transitiontemperature of T_(g)=−35.6° C.

This base polymer was melted in a feeder extruder (single-screwconveying extruder from Troester GmbH & Co. KG, Germany) and conveyed inthe form of polymer melt by this extruder, via a heatable hose, into aplanetary roller extruder from Entex (Bochum). Via a metering port, themelted resin Dertophene T 110 was then added, giving the melt a resinconcentration of 28.3 weight %. Also added was the crosslinker PolypoxR16. Its concentration in the melt was 0.14 weight %. All of thecomponents were mixed to form a homogeneous polymer melt.

By means of a melt pump and a heatable hose, the polymer melt wastransferred to a twin-screw extruder (from Berstoff). There theaccelerator Epikure 925 was added. Its concentration in the melt was0.14 weight %. The entire polymer mixture was then freed from all gasinclusions in a vacuum dome under a pressure of 175 mbar. Downstream ofthe vacuum zone, the microballoons were metered in and were incorporatedhomogeneously into the polymer mixture by means of a mixing element.Their concentration in the melt was 0.7 weight %. The resulting meltmixture was transferred into a die.

Following departure form the die, in other words after a drop inpressure, the incorporated microballoons underwent expansion, with thedrop in pressure producing shear-free cooling of the polymer material.This gave a foamed polyacrylate PSA, which was subsequently shaped toweb form in a thickness of 0.8 mm, using a roll calender, and wasenclosed in a double-sidedly siliconized release film (50 μm,polyester), while the chemical crosslinking reaction went on. Afterbeing wound up, the film is stored at room temperature for at least twoweeks, before being used further for adhesive tape production inaccordance with the invention.

An example polvacrvlate PSA 2 (abbreviated designation in the examples:AC2) was prepared as follows:

a 100 l glass reactor conventional for radical polymerizations wascharged with 4.8 kg of acrylic acid, 11.6 kg of butyl acrylate, 23.6 kgof 2-ethylhexyl acrylate, and 26.7 kg of acetone/benzine 60/95 (1:1).After nitrogen gas had been passed through the reactor for 45 minutes,with stirring, the reactor was heated to 58° C. and 30 g of AlBN wereadded. Thereafter the external heating bath was heated to 75° C. and thereaction was carried out constantly at this external temperature. Aftera reaction time of 1 hour a further 30 g of AlBN were added. After 4hours and 8 hours, the batch was diluted with 10.0 kg each time ofacetone/benzine 60/95 (1:1) mixture. To reduce the residual initiators,90 g portions of bis(4-tert-butylcyclohexyl)peroxydicarbonate were addedafter 8 hours and again after 10 hours. After a reaction time of 24hours, the polymerization was discontinued and the batch was cooled toroom temperature. The polyacrylate was subsequently blended with 0.2weight % of the crosslinker Uvacure® 1500, diluted to a solids contentof 30% with acetone, and then coated from solution onto a double-sidedlysiliconized release film (50 μm, polyester) (coating speed 2.5 m/min,drying tunnel 15 m, temperatures: zone 1: 40° C., zone 2: 70° C., zone3: 95° C., zone 4: 105° C.). The thickness was 50 μm. After being woundup, the film is stored at room temperature for at least two weeks,before being used further for adhesive tape production in accordancewith the invention.

The polyacrylate PSAs, described by way of example in terms of theircomposition and preparation methodology, are described comprehensivelyin DE 10 2010 062 669. The disclosure content of that specification isexplicitly incorporated into the disclosure content of the presentinvention.

The raw materials used for preparing the polyurethane PSA were asfollows:

Mean number- OH number or average NCO number molar mass (mmol OH/kgManufac- Trade name Chemical basis M_(n) (g/mol) or mmol NCO/kg)turer/supplier Voranol P 400 ® Polypropylene glycol, 400 4643 Dow diolVoranol CP Polypropylene glycol, 6000 491 Dow 6055 ® triol MPDiol ®2-methyl- 90.12 22193 Lyondell 1,3-propanediol Vestanat IPDI ®Isophorone 222.3 8998 Degussa diisocyanate (IPDI) Desmodur W ®Dicyclohexylmethane 262 7571 Bayer diisocyanate (HMDI) Coscat 83 ®Bismuth Caschem trisneodecanoate CAS No. 34364-26-6

An example polyurethane PSA (abbreviated designation in the examples: PU1) was prepared as follows:

First of all a pressure-sensitively adhesive, hydroxyl-functionalizedpolyurethane hotmelt prepolymer was prepared by homogenously mixing andthus chemically reacting the following starting materials in theproportions indicated:

TABLE 2 Composition of the hydroxyl-functionalized polyurethane hotmeltprepolymer, example 1 Percentage ratio of Percentage ratio of Percentageratio of the number of OH the number of all Weight the number of OHgroup-bearing functionalized Starting fraction groups to one moleculesto one molecules to one material (weight %) another another (idealized)*another (idealized)* Voranol P 21.7 42.0 43.4 22.5 400 Voranol CP 48.910.0 6.9 3.6 6055 MP Diol 5.2 48.0 49.7 25.7 Coscat 83 0.1 Vestanat 24.148.2 IPDI Total 100.0 100.0 100.0 100. *Calculated from the weightfractions and OH numbers or NCO numbers of the starting materials,subject to the highly idealized assumption that the Voranol P 400 has afunctionality of exactly 2 and the Voranol CP 6055 has a functionalityof exactly 3.

First of all, all of the starting materials listed, apart from the MPDiol and the Vestanat IPDI, were mixed at a temperature of 70° C. undera pressure of 100 mbar for 1.5 hours. The MP Diol was then mixed in over15 minutes, followed by the Vestanat IPDI, likewise over a period of 15minutes. The heat of reaction caused the mixture to heat up to 100° C.,at which point it was transferred to a storage vessel.

The NCO/OH ratio was 0.90. The theoretical gel point is calculated to0.91. The resulting prepolymer was solid at room temperature and interms of consistency was rubberlike and pressure-sensitively adhesive(inherently tacky). The complex viscosity η* at room temperature (23°C.) was 18 000 Pas and at 70° C. was 210 Pas.

The weight-average mean molar mass M_(w) was 120 000 g/mol, the meannumber-average molar mass M_(n) 17 600 g/mol.

The resulting prepolymer was meltable.

To produce a pressure-sensitively adhesive carrier layer crosslinkedchemically by thermal initiation, the prepolymer was suppliedcontinuously to a twin-screw extruder preheated to 80° C. Thecrosslinker was metered continuously, at the same time and at the samelocation, into the twin-screw extruder. The crosslinker used wasDesmodur W (dicyclohexylmethane diisocyanate).

A total NCO/OH ratio of 1.05 was established.

The mixing ratios were therefore as follows:

100 parts by weight prepolymer: 4.54 parts by weight Desmodur W.

Mixing and conveying took place continuously. The time taken for theextrudate to emerge from the extruder was approximately two minutes.

The extrudate was supplied directly to a two-roll applicator, in whichit was coated between two convergent, double-sidedly siliconizedpolyester sheets and thus shaped to form a film. The thickness of thefilm was 0.8 mm. After cooling to room temperature, the film was woundup, following the removal beforehand of one of the two siliconizedpolyester sheets. The wound film was stored at room temperature for atleast two weeks, before being used further for adhesive tape productionin accordance with the invention. G′ at 1 rad/sec and 23° C. was 120 000Pa, G″ at 1 rad/sec and 23° C. was 90 000 Pa, G′ at 10 rad/sec and 23°C. was 360 000 Pa, and G″ at 10 rad/sec and 23° C. was 200 000 Pa.

The following thermoplastic polymers were used for producing layer B:

Designation in Manufac- the examples Trade name turer Manufacturerdescription TP1 Polypro- Borealis Heterophase polypropylene pylenecopolymer without slip or BA 110 CF antiblock additives, DSC meltingtemperature: 158° to 162° C. TP2 Polypro- Borealis Heterophasepolypropylene pylene copolymer without slip or BHC 5012 antiblockadditives, DSC melting temperature: 158° to 162° C. TP3 Desmomelt BayerHighly crystalline, elastic 530 polyurethane with very lowthermoplasticity, minimum activation temperature about 55° C. TP4 EpacolEpaflex Thermoplastic polyurethane of TK 42 high crystallinity,activation temperature: 55° to 60° C. TP5 Platamid M Arkema Highmolecular mass 1276 T copolyamide of nylon type in pellet form, m.p.110° to 115° C. (DIN 53736, method A)

Shaping operations to give a film in a respective thickness of 50 μmtook place by means of a conventional single-screw extruder. In the caseof the Polypropylene BA 110 CF, the films produced from it were obtainedfrom Renolit AG, Salzgitter. This film had been air corona-pretreated byRenolit.

The physical treatments of the layer A were carried out in aroll-to-roll process with a corona unit featuring a Corona-Plusgenerator from Vetaphone A/S (Denmark) with a conventional DBDconfiguration. Insertion cassettes with metal-electrode blades 0.6 mwide and a grounded, silicone-clad roll were used. The distance of theelectrodes from the roll was 2.0 mm. Treatments took place with a webspeed of 20 m/min. The electrode housing was flooded with the respectiveprocess gas, with a gas flow rate of 20 m³/h. The residual oxygencontent of the process gas atmosphere was always <10 ppm oxygen.

As an alternative it would also be possible, without restriction, to useanother commercially available unit for the treatment with process gascorona, as for example a unit with the designation Aldyne™ from SOFTALCorona & Plasma GmbH (Germany). Alternatively, the correspondingphysical pretreatments of the layer A, at least in a nitrogenatmosphere, could also be carried out with a homogeneous, indirectatmospheric pressure plasma. For that purpose it would be possible touse an FG5001 laboratory unit from Plasmatreat GmbH (Steinhagen) with anRD1004 rotational nozzle, with a rate of transit of layer A (web speed)of 5 m/min at a distance of 10 mm from the surface of layer A. Nosubstantial differences have been found.

To produce double-sided adhesive tapes of the invention, the crosslinkedPSA layers produced and the thermoplastic polymer layers were combinedwith one another in the manner below and immediately after physicalpretreatment of the PSA layers, under a process gas atmosphere, werebrought into contact with one another by lamination at room temperature.

EXAMPLES

Layer Layer Layer Corona dose A B C Process gas (W*min/m²) Example 1 AC1 TP 1 Nitrogen 35 Example 2 AC 1 TP 1 Nitrogen 70 Example 3 AC 1 TP 1Carbon dioxide 35 Example 4 AC 1 TP 1 Carbon dioxide 70 Example 5 AC 1TP 1 Argon 35 Example 6 AC 1 TP 1 Argon 70 Example 7 AC 1 TP 2 Nitrogen35 Example 8 AC 1 TP 2 Nitrogen 70 Example 9 AC 1 TP 3 Nitrogen 35Example 10 AC 1 TP 3 Nitrogen 70 Example 11 AC 1 TP 4 Nitrogen 35Example 12 AC 1 TP 4 Nitrogen 70 Example 13 AC 1 TP 5 Nitrogen 35Example 14 AC 1 TP 5 Nitrogen 70 Example 15 PU 1 TP 1 AC 2 Nitrogen 35Example 16 PU 1 TP 1 AC 2 Nitrogen 70 Example 17 PU 1 TP 1 AC 2 Carbondioxide 35 Example 18 PU 1 TP 1 AC 2 Carbon dioxide 70 Comparative AC 1TP 1 Nitrogen 70 Example 1 uncross- linked Comparative AC 1 TP 1 Air 70Example 2

Test Results: Peel Strength:

In the peel strength test, in examples 1 to 18, there was alwayscohesive failure found within the layer A. In example 7, in a smallnumber of specimens, there was predominantly cohesive failure, withslight (around 10%) proportions of adhesive failure between layers A andB. In examples 1 to 14, the force which led to the cohesive failure ofthe layer A, i.e., the splitting force, was 25 to 30 N/cm. In examples15 to 18, the splitting force was 38 to 42 N/cm.

In comparative examples 1 and 2, there was adhesive failure between thelayers A and B. After a) and b) storage for determining the agingcharacteristics, there was again always cohesive failure within thelayer A in examples 1 to 18, although the splitting forces were reducedby 20% to 30% relative to the figures reported above.

Shear Test:

In the shear test, in examples 1 to 18, there was always cohesivefailure found within the layer A. In examples 1 to 14, the holding powerat room temperature was 100 to 500 minutes. In examples 15 to 18, theholding power at room temperature was 2500 to 10 000 minutes. Examples15 to 18 were also tested at 70° C. There as well there was cohesivefailure within the layer A. The holding powers were 200 to 400 minutes.

In comparative examples 1 and 2, there was adhesive failure between thelayers A and B.

1. A double-sided adhesive tape having a first outer pressure-sensitiveadhesive side and a second outer heat-activatable side, comprising an atleast two-layer product system composed of layers A and B, layer A beinga layer of pressure-sensitive adhesive crosslinked chemically by thermalinitiation, or a pressure-sensitively adhesive carrier layer crosslinkedchemically by thermal initiation, layer B being a layer based on athermoplastic polymer, layer A and layer B being in direct contact withone another, and the surface of layer A that is in direct contact withlayer B having been corona- or plasma-pretreated, wherein the corona orplasma pretreatment has taken place in an atmosphere of nitrogen, carbondioxide, or a noble gas, or a mixture of at least two of these gases. 2.The double-sided adhesive tape as claimed in claim 1, wherein thesurface of the layer A that is in contact with layer B has been corona-or plasma-pretreated in the chemically crosslinked state.
 3. Thedouble-sided adhesive tape as claimed in claim 1, wherein no additionalactinic or ionizing radiation is used for crosslinking layer A.
 4. Thedouble-sided adhesive tape as claimed in claim 1, wherein layer A is alayer produced in a hotmelt process.
 5. The double-sided adhesive tapeas claimed in claim 1, wherein layer A is a layer based on polyacrylate.6. The double-sided adhesive tape as claimed in claim 1, wherein layer Ais a layer based on polyurethane.
 7. The double-sided adhesive tape asclaimed in claim 1, wherein layer A is foamed or has a foamlikeconsistency.
 8. The double-sided adhesive tape as claimed in claim 1,wherein the surface of the layer A that is not in direct contact withlayer B is in direct contact with a further layer or with a furtherlayer sequence, the outer layer being a layer of pressure-sensitiveadhesive.
 9. The double-sided adhesive tape as claimed in claim 1,wherein layer B is a layer based on a polyolefin or a polyolefinmixture.
 10. The double-sided adhesive tape as claimed in claim 1,wherein layer B is a layer based on a polypropylene copolymer or amixture of a polypropylene copolymer and another polyolefin.
 11. Thedouble-sided adhesive tape as claimed in claim 1, wherein layer B has amelting temperature as determined by DSC of between 140° C. inclusiveand 180° C. inclusive.
 12. The double-sided adhesive tape as claimed inclaim 1, wherein the surface of the layer B that is contact with layer Ahas been air corona-pretreated.
 13. A method for producing adouble-sided adhesive tape as claimed in claim 1, comprising bringinglayer A and layer B into direct contact with one another in a backing orlaminating operation which takes place immediately following a corona orplasma pretreatment.
 14. A combination comprising (A) double-sidedadhesive tape as claimed in claim 1 and (B) an article composed of athermoplastic polymer, of EPDM, or of another rubberlike material.
 15. Amethod for adhesively bonding profiles composed of EPDM or of anotherrubberlike material, said method comprising bonding double-sidedadhesive tape as claimed in claim 1 to said EPDM or another rubberlikematerial.